Except that working in/with Vanderbilt tenders is a royal PITA.
I just did three ERR upgrades on 3rd Rail locomotives with the Vanderbilt tender, and I have one more to go, all for the same customer. I can assure you, they're a PITA! However, it's not quite like a ship in a bottle, the bottom frame does drop out and allow you to work on it. There are some designs, I think maybe a weaver or Williams, that you did indeed have to work from one end.